Update release-information for v2.2 Release ...

Removed deprecated interfaces that have been removed from the TF-A
project, updated the deprecated list with new deprecations for v2.2
Release, added upcoming release information, remove mentions of PR from
github.

Signed-off-by: Lauren Wehrmeister <lauren.wehrmeister@arm.com>
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
Change-Id: I2b59d351cde9860ad0dcb6520a8bd2827ad403cf

doc: Move "About" content from index.rst to a new chapter ...

The index.rst page is now the primary landing page for the TF-A
documentation. It contains quite a lot of content these days,
including:

- The project purpose and general intro
- A list of functionality
- A list of planned functionality
- A list of supported platforms
- "Getting started" links to other documents
- Contact information for raising issues

This patch creates an "About" chapter in the table
of contents and moves some content there. In order,
the above listed content:

- Stayed where it is. This is the right place for it.
- Moved to About->Features
- Moved to About->Features (in subsection)
- Stayed where it is. Moved in a later patch.
- Was expanded in-place
- Moved to About->Contact

Change-Id: I254bb87560fd09140b9e485cf15246892aa45943
Signed-off-by: Paul Beesley <paul.beesley@arm.com>